Purpose :
A detailed description of the biomechanical relationship between angle narrowing and elevated intraocular pressure has long eluded clinicians and researchers. Gonioscopy is the current gold standard in the evaluation of narrow angles although its correlation with intraocular pressure is poor. Subtle differences in angle dimensions are also difficult to quantify with gonioscopy. Recent work has demonstrated a strong correlation between intraocular pressure and AS-OCT measurements of angle recess area (ARA) in subjects with elevated intraocular pressure. This relationship manifests only for ARA values below a certain threshold which creates a novel OCT-based definition of "narrow." This study examines the number of eyes with sub-threshold sectoral ARA values in subjects with elevated intraocular pressure (IOP) and the relationship between ARA and IOP as sectoral ARA values decrease.

Methods :
We analyzed four AS-OCT images from one eye each of 102 subjects with IOP greater than 21. All subjects were selected from the Chinese American Eye Study (CHES) – a population based study of Chinese Americans in Los Angeles, CA. We measured ARA values 500 micrometers from the scleral spur (ARA500) for each of eight sections through the angle. We calculated the number of eyes with a sectoral ARA500 of less than 0.45 mm2, which has previously been shown to be the mean threshold below which intraocular pressure begins to rise, as well as intraocular pressure for sectoral thresholds of 0.9, 0.45, 0.22, and 0.11 mm2.

Results :
The eight sectors of the angle had different numbers of subjects with sub-threshold ARA500 values: superior (44), superonasal (36), inferonasal (30), superotemporal (26), inferior (25), inferotemporal (14), and temporal (12). As the mean ARA500 values decreased, there was asymmetric narrowing of the eight sectors. Lower sectoral ARA500 thresholds in the inferior, inferotemporal, and temporal sectors had a more profound impact on IOP compared to the other sectors.

Conclusions :
The results of this study suggest that the narrowest portions of the angle in an open angle are the most likely to close in a narrow angle. Additionally, closure of the most open portions of the angle is correlated with the highest intraocular pressure likely due to associated closure of other more narrow portions of the angle.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.